1. Field of the Invention
The present invention generally relates to a synchronization system, a synchronization method, and a recording medium, and more particularly, to a synchronization system and a synchronization method which realize strict commercial time synchronization by advancing the timing of generation of a PN (Pseudo-random Noise) signal in a upstream station by a transmission line delay.
2. Description of the Related Art
Hereinafter, a conventional commercial time synchronization system will be described. An exchange and a first radio station are connected to each other through a first transmission line. The aforementioned exchange and a second radio station are connected to each other through a second transmission line.
For example, 1.5-megabits-per-second (Mbps) high-speed digital commercial transmission lines are used as the aforementioned first and second transmission lines. A master station of a time synchronization system is the exchange. Time in (or operating timing of) each of the aforementioned first and second radio stations is controlled by the aforesaid exchange.
Transmission information data is transmitted by being divided into frames. The frame length of frames is set at, for instance, 20 milliseconds (msec). Further, time synchronization is realized by time synchronization bits (or frame synchronization bits) periodically sent from the aforementioned exchange to the aforesaid first and second transmission lines.
The aforementioned exchange is operative to send a frame synchronization bit every frame period. The aforesaid first and second radio stations are operative to establish frame synchronization by detecting frame synchronization bits sent from the aforementioned exchange, and to extract transmission information data. Further, the aforementioned first and second radio stations are adapted to operate by employing a signal indicating the timing of detection of a frame synchronization bit as a master timing signal.
Therefore, the operation timing of a upstream station differs from that of a downstream station by a transmission line delay. Usually, the transmission line delay is several msec or so. In the case of this conventional system, commercial synchronization can be realized with such a degree of accuracy that this transmission line delay is allowed.
Thus, according to a conventional commercial synchronization method, the operation timing of a upstream station differs from that of a downstream station by a transmission line delay. Consequently, the conventional commercial synchronization method has a drawback in that commercial synchronization cannot be realized with accuracy higher than that achieved by allowing the transmission line delay.
The present invention is accomplished in view of such circumstances. Accordingly, an object of the present invention is to realize strict commercial time synchronization with such a degree of accuracy that a transmission delay comparable to the transmission rate of a transmission line is allowed.
To achieve the foregoing object, according to an aspect of the present invention, there is provided a synchronization system for synchronizing first and second devices. The aforesaid first device comprises first PN signal generating means for generating a PN signal in synchronization with a predetermined timing signal, first multiplexing means for transmitting a multiplexing signal obtained by multiplexing transmission information data to be transmitted and the aforesaid PN signal, first demultiplexing means for receiving a signal transmitted from the aforesaid second device and for demultiplexing the received signal into the transmission information data and the PN signal, and first detection means for detecting a first timing error that is an error between the aforesaid PN signal, which is obtained by demultiplexing by the aforesaid first demultiplexing means, and the aforesaid PN signal generated by the aforesaid first PN signal generating means.
The aforesaid second device comprises second PN signal generating means for generating a PN signal in synchronization with a predetermined timing signal, second multiplexing means for transmitting a multiplexing signal obtained by multiplexing transmission information data to be transmitted and the aforesaid PN signal, second demultiplexing means for receiving a signal transmitted from the aforesaid first device and for demultiplexing the received signal into the transmission information data and the PN signal, and second detection means for detecting a first timing error that is an error between the aforesaid PN signal, which is obtained by demultiplexing by the aforesaid second demultiplexing means, and the aforesaid PN signal generated by the aforesaid second PN signal generating means.
The aforesaid first PN signal generating means shifts operation timing thereof by a time corresponding to half the first timing error detected by the aforesaid first detection means. The aforesaid second PN signal generating means corrects operation timing thereof in such a way as to eliminate the aforesaid second timing error detected by the aforesaid second detection means.
Further, in the case of an embodiment of this synchronization system, the aforesaid first device further comprises first timing signal generating means for generating a predetermined timing signal. The aforesaid second device further comprises second timing signal generating means.
In this embodiment, the aforesaid first PN signal generating means determines an operation timing thereof in synchronization with a timing signal generated by the aforesaid first timing signal generating means. The aforesaid second PN signal generating means determines operation timing thereof in synchronization with a timing signal generated by the aforesaid second timing signal generating means.
Furthermore, in the case of another embodiment of the synchronization system, the aforesaid first multiplexing means transmits arbitrary N bits data, which are represented by a PN signal generated by the aforesaid first PN signal generating means, when transmission information data to be transmitted is not present. The aforesaid second multiplexing means transmits arbitrary N bits data, which are represented by a PN signal generated by the aforesaid second PN signal generating means, when there is no transmission information data to be transmitted.
Moreover, in the case of another embodiment of the synchronization system, the aforesaid first and second multiplexing means transmit predetermined discrimination information immediately before a PN signal is transmitted. The aforesaid first and second demultiplexing means regard signals transmitted immediately after the aforesaid discrimination information as PN signals.
Furthermore, in the case of another embodiment of the synchronization system, the aforesaid first detection means detects the aforesaid first timing error by searching a pattern of one period of a PN signal, which is generated by the aforesaid first PN signal generating means, for a consecutive N-bit pattern matching an N-bit pattern represented by a PN signal obtained by demultiplexing by the aforesaid first demultiplexing means. The aforesaid second detection means detects the aforesaid second timing error by searching a pattern of one period of a PN signal, which is generated by the aforesaid second PN signal generating means, for a consecutive N-bit pattern matching an N-bit pattern represented by a PN signal obtained by demultiplexing by the aforesaid second demultiplexing means.
Additionally, in the case of another embodiment of the synchronization system, timing control is performed so that a pattern represented by a PN signal, which is generated by the aforesaid first PN signal generating means of said first device at a time point (txe2x88x92xcfx84) where xcfx84 designates a time period during which transmission information data is transmitted from the aforesaid first device to the aforesaid second device, and t denotes a current time point, matches a pattern represented by a PN signal, which is generated by the aforesaid second PN signal generating means of the aforesaid second device at the point in time t.
Further, according to another aspect of the present invention, there is provided a synchronization method having a first process to be performed in a first device and a second process to be performed in a second device, for synchronizing the aforesaid first and second devices. The aforesaid first process comprises a first PN signal generating step of generating a PN signal in synchronization with a predetermined timing signal, a first multiplexing step of transmitting a multiplexing signal obtained by multiplexing transmission information data to be transmitted and the aforesaid PN signal, a first demultiplexing step of receiving a signal transmitted from the aforesaid second device and demultiplexing the received signal into transmission information data and a PN signal, and a first detection step of detecting a first timing error that is an error between said PN signal, which is obtained by demultiplexing at the aforesaid first demultiplexing step, and the aforesaid PN signal generated at the aforesaid first PN signal generating step.
The aforesaid second process comprises a second PN signal generating step of generating a PN signal in synchronization with a predetermined timing signal, a second multiplexing step of transmitting a multiplexing signal obtained by multiplexing transmission information data to be transmitted and the aforesaid PN signal, a second demultiplexing step of receiving a signal transmitted from the aforesaid first device and demultiplexing the received signal into transmission information data and a PN signal, and a second detection step of detecting a second timing error that is an error between the aforesaid PN signal, which is obtained by demultiplexing at the aforesaid second demultiplexing step, and the aforesaid PN signal generated at the aforesaid second PN signal generating step.
At the second PN signal generating step, PN-signal generation timing is corrected in such a manner as to eliminate the aforesaid second timing error detected at the aforesaid second detection step. At the aforesaid first PN signal generating step, PN-signal generation timing is shifted ahead by a time period corresponding to half the first timing error detected at the aforesaid first detection step.
Furthermore, according to another aspect of the present invention, there is provided a recording medium on which a program having a first process to be performed in a first device and a second process to be performed in a second device is recorded for synchronizing said first and second devices.
The aforesaid first process comprises a first PN signal generating step of generating a PN signal in synchronization with a predetermined timing signal, a first multiplexing step of transmitting a multiplexing signal obtained by multiplexing transmission information data to be transmitted and the aforesaid PN signal, a first demultiplexing step of receiving a signal transmitted from the aforesaid second device and demultiplexing the received signal into transmission information data and a PN signal, and a first detection step of detecting a first timing error that is an error between the aforesaid PN signal, which is obtained by demultiplexing at the aforesaid first demultiplexing step, and the aforesaid PN signal generated at the aforesaid first PN signal generating step.
The aforesaid second process comprises a second PN signal generating step of generating a PN signal in synchronization with a predetermined timing signal, a second multiplexing step of transmitting a multiplexing signal obtained by multiplexing transmission information data to be transmitted and the aforesaid PN signal, a second demultiplexing step of receiving a signal transmitted from the aforesaid first device and demultiplexing the received signal into transmission information data and a PN signal, and a second detection step of detecting a second timing error that is an error between the aforesaid PN signal, which is obtained by demultiplexing at the aforesaid second demultiplexing step, and the aforesaid PN signal generated at the aforesaid second PN signal generating step.
At the aforesaid second PN signal generating step, PN-signal generation timing is corrected in such a manner as to eliminate the aforesaid second timing error detected at the aforesaid second detection step.
At the aforesaid first PN signal generating step, PN-signal generation timing is shifted ahead by a time period corresponding to half the first timing error detected at the aforesaid first detection step.